With the raising of the concept of the Carrier Ethernet (CE), the connection oriented Ethernet technique—the Provider Backbone Transport (PBT) is also implemented in October, 2005 for the purpose of satisfying the requirement of the telecommunication network. Afterwards, there are both domestic and foreign providers using the PBT technique to network, which provides a very good beginning for the development of the PBT technique in the metropolitan area network.
The basis of the PBT technique is the Provider Backbone Bridge (PBB) technique defined in the IEEE 802.1ah, and the IEEE calls the PBT technique the Provider Backbone Bridge Traffic Engineering (PBB-TE) technique. The PBB-TE technique is on a basis of the PBB technique, and its core is to improve the PBB technique. The source device of the CE inserts a Backbone Destination Medium Access Control (MAC) Address (B-DA), a Backbone Source MAC Address (B-SA), a Backbone Virtual Local Area Network (B-VLAN) identity (ID) and a Service Instance TAG (I-TAG) into the header of the message. The forwarding path between the source device and the destination device of the CE is statically configured in advance, and the in-between CE device can forward the data frame based on the B-DA and B-VID in the forwarding list, of which the forwarding efficiency is high.
In order to make the Ethernet achieve the carrier-grade standard, the PBB-TE usually uses the protection technique. FIG. 1 shows a schematic diagram 1 of the end to end tunnel protection principle of PBB-TE in the prior art, wherein the end to end primary tunnel of a certain traffic engineering service instance is TN 1: PE 1← →P1← →P2← →P3← →PE 2, and PE1 and PE2 are ends of this tunnel instance; TN2: PE 1← →P5← →P6← →PE 2 is an end to end secondary tunnel of this traffic engineering service instance, and in order to differentiate the above primary tunnel TN1 and the secondary tunnel TN2, B-VLAN1 is specified for the primary tunnel TN1 and B-VLAN2 is specified for the secondary tunnel TN2 during the pre-configuration. When a fault occurs in the end to end primary tunnel TN1, the data stream can be switched into the secondary tunnel TN2.
The PBB-TE uses the Connectivity Fault Management (CFM) mechanism in the IEEE 802.1ag to continuously monitor the tunnel state in the network. When the primary tunnel fails, the service is automatically switched into the secondary tunnel established in advance, which implements the tunnel protection technique.
In the prior art, the tunnel continuity is detected by sending the Continuity Check Message (CCM) defined in the IEEE 802.1ag in the tunnel. As shown in FIG. 2, the tunnel ends PE1 and PE2 respectively send the CCM to each other along with the primary tunnel TN1 and the secondary tunnel TN2, the primary tunnel and the secondary tunnel respectively belong to the different Maintenance Associations (MA), the primary tunnel belongs to MA1, the secondary tunnel belongs to MA2, and CCMs of the primary tunnel and the secondary tunnel respectively encapsulates the ID of the B-VLAN1 and the ID of the B-VLAN2. This method implements the full path protection of the tunnel.
Although the end to end protection technique of the PBB-TE is able to efficiently protect the tunnel, this end to end protection scheme not only has a longer protection switching time, but also involves too many nodes. Therefore, the IEEE organization proposes the protection scheme of the PBB-TE. As shown in FIG. 3, P1-P2-P3 is a physical link bearing a path of the end to end primary tunnel TN1 (PE 1← →P1← →P2← →P3← →PE 2), and the physical link is called as the segment in the following text. The secondary segment (P1-P4-P3) can be used for the protection. The main difference of the segment protection scheme of the PBB-TE and the end to end protection of the PBB-TE is that: the segment protection scheme is on the basis of the protection of the physical link, whereas the end to end protection scheme is on the basis of the protection of the tunnel.
In order to implement the segment protection function of the PBB-TE, the integrity of the CCM messages are required to be verified on the primary segment and the secondary segment of the segment protection domain at the same time. As shown in FIG. 4, the ends P1 and P3 respectively send CCMs to each other along with the primary segment (P1-P2-P3) and the secondary segment (P1-P4-P3), the primary segment belongs to MA3, the secondary segment belongs to MA4, and the CCMs of the primary segment and the secondary segment respectively encapsulates the corresponding IDs of the B-VLANs. This method implements the good protection for the path (the physical path) of the tunnel.
The case that there is a shared link between the segment protection domains of the PBB-TE is a hot topic discussed in the current segment protection. The segment protection domain is the segment protection domain of the tunnel (Ethernet Switched Path, ESP), as shown in FIG. 5, the segment protection domain 1 formed by the segment A-B-M-E-F-A, which is also called the first segment protection domain, and the segment protection domain 2 formed by the segment C-B-M-E-D-C, which is also called [as] the second segment protection domain, are both the segment protection domains of ESP 1<X, Y, 1> and ESP 2<Y, X, 2> (the attribute of the ESP is marked by the triple of <ESP-DA, ESP-SA, ESP-VID> in the data stream, referring to IEEE 802.1Qay). The segment protection domain 1 and the segment protection domain 2 have the shared path B-M-E. In the segment protection domain 1, the primary segment of ESP1 and ESP2 is A-B, and the secondary segment is A-F-E-M-B; in the segment protection domain 2, the primary segment of ESP1 and ESP2 is C-B, and the secondary segment is C-D-E-M-B.
In order to implement the above segment protection function with the shared link topology, the prior art provides a solution. As shown in FIG. 6, in order to perform the segment protection on ESP 1 and ESP 2, the Primary Interconnecting Bridge (PIB) node and the Alternate Interconnecting Bridge (AIB) node are configured on the shared path B-M-E, the node B is the PIB node, and the node E is the AIB node. Domain Endpoint Bridge (DEB) nodes are configured in the segment protection domain 1 and the segment protection domain 2, and the node A and node C are both the DEB nodes.
As shown in FIG. 6 and FIG. 7, in the segment protection domain 1, the node A (DEB) and the node B (PIB) respectively send the CCM messages on the primary segment (A-B) and the secondary segment (A-F-E-M-B), so as to detect whether the primary segment and secondary segment are normal; the node A (DEB) and the node E (AIB) respectively send the CCM messages on the alternate primary segment and the alternate secondary segment, so as to detect whether the alternate primary segment (A-B-M-E) and alternate secondary segment (A-F-E) are normal. Similarly, in the segment protection domain 2, the node C (DEB) and the node B (PIB) respectively send the CCM messages on the primary segment (C-B) and the secondary segment (C-D-E-M-B), so as to detect whether the primary segment and secondary segment are normal; the node C (DEB) and the node E (AIB) respectively send the CCM messages on the alternate primary segment and the alternate secondary segment, so as to detect whether the alternate primary segment (C-B-M-E) and alternate secondary segment (C-D-E) are normal.
The DEB node only detects the primary segment and the secondary segment in the segment protection domain to which this DEB node belongs, but is not responsible for detecting the alternate primary segment and the alternate secondary segment; the PIB detects the primary segments and the secondary segments in two segment protection domains to which this PIB belongs at the same time; the AIB detects the alternate primary segments and the alternate secondary segments in two segment protection domains to which this AIB belongs at the same time.
As shown in FIG. 8, if a fault occurs on a link between the nodes A and B, the node A (DEB) does not receive the CCM message sent on the primary segment from the node B (PIB) in certain duration, then, see FIG. 6, the node A will switch all the tunnels, for example ESP 1, originally transmitted on the primary segment (A-B) into the secondary segment (A-F-E-M-B). Similarly, the node B (PIB) does not receive the CCM message sent on the primary segment from the node A (DEB) in certain duration either, then, see FIG. 6, the node B will switch all the tunnels, for example ESP 2, originally transmitted on the primary segment (B-A) into the secondary segment (B-M-E-F-A). Finally, the newest paths of the ESP 1 and ESP 2 in two segment protection domains with the shared link respectively become [to] A-F-E-M-B-C and C-B-M-E-F-A.
Although the above main mechanism of the DEB node, PIB node and AIB node is able to solve a majority of problems quite well, the fault is unable to be detected in certain cases, thereby causing the interruption of the communication in long duration. The specific example is as follows:
As shown in FIG. 9, the shared link <B, M> and the link <B, C> of the segment protection domain 2 both have the fault. In the segment protection domain 2, the node C (DEB) does not receive the CCM message sent on the primary segment from the node B (PIB) in certain duration, and the node C will switch all the tunnels, for example ESP 2, on the primary segment of the segment protection domain 1 into the secondary segment; the node E (AIB) does not receive the CCM message sent on the alternate primary segment from the node A (DEB) in certain duration, the node E will switch all the tunnels, for example ESP 2, on the alternate primary segment into the alternate backup segment; therefore, the path of the ESP 2 in segment protection domain 1 and segment protection domain 2 changes into C-D-E-F-A, and the data message can be transmitted normally. However, in segment protection domain 1, since the node A (DEB) is able to receive the CCM message sent on the primary segment from the node B (PIB) in a certain period, the node A will not switch all the tunnels, for example ESP 1, originally transmitted on the primary segment (A-B) into the secondary segment. However, since the shared link <B, M> and link <B, C> both have the fault, therefore, all the data messages in the ESP 1 will be discarded after reaching the node B, thereby causing the interruption of the communication in long duration.
It can be seen from the above analysis that the solution in the prior art will allow the occurrence of the case of severe communication interruption in certain cases, and a new mechanism is required to solve this problem. Therefore, in the segment protection domain with the shared link, it will be quite meaningful to propose a new joint detection scheme to overcome the above drawback.